<!DOCTYPE html>
<html>
    <head>
        <title></title>
        <meta charset="utf-8">
        <script language="JavaScript">
            <!-- 输入 -->
            expr = prompt("请输入要计算的式子", "4 * 250 + 8");	// 数学表达式
            n = eval(expr);	
            alert(expr + " = " + n);	// 显示表达式计算结果
            
        </script>
    
    </head>
    <body>
    
    </body>
</html>
